1. Field of the Invention
The present invention relates generally to an apparatus and method for positioning an automatic guided vehicle having a loading table. More specifically, the present invention relates to an apparatus and method for using the loading table of the automatic guided vehicle to compensate for detected positioning errors of the automatic guided vehicle.
2. Description of the Prior Art
Automatic guided vehicles have greatly been developed as nucleating apparatus of factory automation for these several years.
The conventional automatic guided vehicle has been provided with a table which is loaded with articles to be conveyed, disposed on the top of the vehicle, and conveys the load of articles to stations provided for various processes. The articles are automatically transferred from the automatic guided vehicle to every station by a unloading device provided in the station.
On the other hand, linear and angular degrees of precision in stoppage of the automatic guided vehicle are in the order of .+-.10 mm in the advance direction as well as in the direction intersecting therewith and .+-.1.degree. or so in the rotational direction around a vertical axis, respectively, and relative degrees of precision in stoppage between the unloading device and the loading table have an equal value with those described above, because of dependence thereof on the degree of precision in stoppage of the automatic guided vehicle. Together with precision error at the time of stoppage, deviation occurs between relative stop positions of said unloading device and of the loading table and regular relative stop positions. Therefore, it is required to provide a structure for eliminating said positional deviation for the unloading device or the automatic guided vehicle or to improve stoppage precision of the vehicle such as in the case of automatic unloading of articles in the semiconductor manufacturing factory.
As known measures for improving stoppage precision, there is positioning means of such structure that a plurality of hydraulic jacks are provided for the automatic guided vehicle, conical holes are drilled in rod parts of the jacks, a plurality of conical positioning projections to be engaged with said holes are provided at the regular stop positions on the floors of every station correspondingly to setting positions of the hydraulic jacks, and, upon stoppage of the automatic guided vehicle at the station, the hydraulic jacks are moved forward to be fitted on the respective positioning projections for positioning the vehicle. Thus, the automatic guided vehicle is lifted the floor and positioned in the correct position.
However, in said measures, the positioning projections are obstructive to running of the vehicle and a large number of additional devices such as a hydraulic generating source are required, thereby inviting price increase and more complicated structure. Further, such measures as mentioned above, which determine a position of the vehicle while depending on engagement of holes with projections, degrades positioning precision owing to advanced wear of holes and projections, whereby particles of worn parts are turned into dust and the vehicle could not be employed in circumstances where the degrees of positioning precision and purification are limited such as in the semiconductor manufacturing factory.
Unloading devices, if each provided with a structure for eliminating the aforesaid positional deviation, necessitate a large number of such structures because they are arranged in every station, thereby leading to price increase of the whole system.
In addition, when providing a structure for eliminating the positional deviation for the automatic guided vehicle, it is presumable that positioning in the advance direction of the vehicle and in the direction intersecting therewith depends on ball screws and that positioning in the rotational direction around a vertical axis depends on rotation of gearing mechanism, however, the mechanism using ball screws and gearing has such problems as requiring wide space for installation and a large number of parts, weight increase, and higher manufacturing cost on account of requirements for leveled up precision in component parts to obtain higher precision in the ball screw and gearing mechanisms attended with backlash. The use of the ball screws and gearing mechanism causes particulated dust of worn parts and requires dust-proof countermeasures over a wide range.